Imagine that you walk into a room, where three people are sitting, facing you. Their faces are oriented towards you, but all three of them have their eyes directed towards the left side of the room. You would probably follow their gaze to the point where they were looking (if you weren’t too unnerved to take your eyes off these odd people).

As a social species, we are particularly cued in to social cues like following others’ gazes. However, we’re not the only animals that follow the gazes of members of our species: great apes, monkeys, lemurs, dogs, goats, birds and even tortoises follow each other’s gazes too. However, we don’t all follow gazes to the same extent. One species of macaque monkey (the stumptailed macaque) follows gazes a lot more than other macaque species, bonobos do it more than chimpanzees and human children follow gazes a lot more than other great ape species do.

The stump-tailed macaque follows the gazes of others a lot

Species also differ in their understanding of what the other animal is looking at. For example, if we saw a person gazing at a point, and between them and this point was a barrier, whether the barrier was solid or transparent would affect how far we followed their gaze. This is because we imagine ourselves in their physical position and what they might be able to see. Bonobos and chimpanzees can also do this, but not the orang-utan. Like us, great apes and old world monkeys also will follow a gaze, but then look back at the individual gazing if they don’t see what the individual is gazing at (‘are you going crazy or am I just not seeing what you’re seeing?’). Capuchin and spider monkeys don’t seem to do this.

So, even though a lot of animals are capable of following the gazes of others, there is a lot of variation in the extent and flexibility of this behaviour. A recent study looked to see whether chimpanzees, bonobos, orang-utans and humans would be more likely to follow their own species’ gazes than another species.

To do this, the researchers showed the test subjects videos of either an animal of the same species or of a different species (the ‘model’) looking in a particular direction. The scientists then looked to see if the animal watching the video looked in the same direction as the model. To more easily see where the non-human primates’ gazes fell, the researchers wanted to keep their heads in a particular position (facing straight ahead). To do this, they gave the animals a straw that they could suck on to get grape juice. They filmed these animals, and then used computer software that tracked which direction the individuals’ eyes moved.

Image above: a) the participants of the study, sucking on grape juice to keep their heads still. b) the models of the study, that the participants watched on video

All four primates (the chimpanzees, bonobos, orang-utans and humans) followed the gaze of the model in the video when they were the same species as themselves. This is not surprising, as all of these species are known to follow gazes.

However, while human adults, orang-utans and bonobos all would follow the gaze of both their own species, and of a different species, human infants and chimpanzees only followed the gaze of their own species. Why might this be? Well, the human infants and chimps were particularly inattentive to the videos being shown to them. Therefore, it’s likely that they didn’t follow the gaze of the video demonstrator not because they were incapable of it, but simply because they lacked the motivation to do so. Given this lower level of motivation, it is only the more salient stimulus of seeing their own species on the video that gets them to pay attention.

3 Comments

Eye gaze has some other very fascinating implications in language development for human children. Patricia Kuhl and Andrew Meltzoff have found interesting correlations in eye-gazy following for infants and their language ability years later. http://www.ncbi.nlm.nih.gov/pubmed/16246245/

On the other hand, only the Chimps and Humans might have been cluey enough to know that they were watching a video, so that the gaze direction of the model in the video was not salient to anything much at all.

I do think that for any realistic findings you would need to use a model in the same room/space as the animal being tested.

Then if the photos shown on this article were the ones use, and the test was to see which ‘spot’ the subjects looked at — ONLY the bonobo was looking AT the spot. The chimp, orang-utan and human were merely facing to the right in the photo, but not actually apparently ‘looking’ at anything.

So I would have failed – initially I ONLY saw the spots on the Bonobo photo.
The chimp seemed to be looking down at the right hand bottom corner, the orang-utan seemed to be looking at himself in a mirror, and the human seemed to be looking at someone or something in the distance – not anywhere in the picture, anyway.

You’re right that the results would be more powerful using real demonstrators- only I’d imagine it would be hard to get most animals (and human infants) to look in the direction you want them to look when they’re being watched by another individual, and not be distracted by that individual (especially if it’s a social species as these all are). Using a video has its limitations, but at least you know that all the individuals you’re testing are seeing what you want them to see, and seeing the same thing as each other.

You’re also right in that you have to be sure that it’s not something about a particular video that’s causing the effect you see, rather than the species in question. In this experiment I think they only used one individual as a model to represent the species, and this could indeed skew the results.